The internal dynamical equilibrium of H II regions: A statistical study

¹ Instituto de Astrofísica de Canarias, C. Vía Láctea s/n, 38200 La Laguna, Tenerife, Spain e-mail: [mpastor;corrado]@ll.iac.es
² Consejo Superior de Investigaciones Científicas (CSIC), Spain e-mail: jeb@ll.iac.es
³ Dpto. de Física Teórica y del Cosmos, Facultad de Ciencias, U. de Granada, Avda. Fuentenueva s/n, 18071 Granada, Spain e-mail: azurita@ugr.es
⁴ Isaac Newton Group of Telescopes, Apartado de Correos 321, 38700 Santa Cruz de La Palma, Canarias, Spain
⁵ Observatorio Astronómico Nacional (UNAM), Apartado Postal 877, Ensenada, B.C., México e-mail: mrozas@astrosen.unam.mx

Received: 19 March 2004
Accepted: 14 October 2004

Abstract

We present an analysis of the integrated Hα emission line profiles for the H ii region population of the spiral galaxies NGC 1530, NGC 6951 and NGC 3359. We show that ~70% of the line profiles show two or three Gaussian components. The relations between the luminosity () and non-thermal line width () for the H ii regions of the three galaxies are studied and compared with the relation found taken all the H ii regions of the three galaxies as a single distribution. In all of these distributions we find a lower envelope in log . A clearer envelope in is found when only those H ii regions with are considered, where is a canonical estimate of the sound speed in the interestellar medium. The linear fit for the envelope is where the Hα luminosity of the region is taken directly from a photometric H ii region catalogue. When the Hα luminosity used instead is that fraction of the H ii region luminosity, corresponding to the principal velocity component, i.e. to the turbulent non-expanding contribution, the linear fit is , i.e. unchanged but slightly tighter. The masses of the H ii regions on the envelope using the virial theorem and the mass estimates from the Hα  luminosity are comparable, which offers evidence that the H ii regions on the envelope are virialized systems, while the remaining regions, the majority, are not in virial equilibrium.